Rational Synthesis of Three-Dimensional Nanosuperstructures for Applications in Energy Storage and Conversion

The ever-increasing fossil fuel demand with aroused environmental problems drives the intensive exploration of renewable and environmentally benign energy technologies. Due to the unique chemical and physical properties, 3-D nanostructure materials received particular attention for energy storage and conversion devices. However, the synthesis of 3-D nanosuperstructures (NSSs) remains a daunting task. In this mini review, we will discuss some recent achievements in rational and innovative approaches for fabricating NSSs assisted by designed catalysts both in aqueous solutions and vapor phases. Two types of 3-D NSSs are demonstrated; one is semiconductor ZnO, and the other is graphene/thin graphite, both of which show high crystallinity and controlled dimensions in 3-D. The obtained 3-D ZnO NSSs were applied for enhancing solar-assisted water oxidation efficiency, which offer 150% improvement compared with simple nanowire arrays obtained at the same condition by using the commonly employed 0-D dot catalysts. The 3-D freestanding thin graphite with two levels of porosity was functionalized with thin nickel hydroxide nanoplates [Ni(OH)(2)] and applied as electrodes for alkaline batteries. The electrodes are binder-free and provide a remarkable discharge capacity of 480 mA h g(-1) at a rate of 1.5 A g(-1). Compared with previous reports, they also exhibit excellent cyclability with 97.5% capacitance retention after 4000 cycles. The synthesis mechanism of 3-D superstructures could inspire the manufacturing of 3-D nanomaterials with high efficiency, large scales, and controllability.